1. Field of the invention
The present invention relates generally to a vehicle-use surroundings monitoring system and more particularly to a vehicle-use surroundings monitoring system which monitors the surroundings of a vehicle for giving alarm to a driver by detecting another vehicle approaching from the surroundings of the subject traveling vehicle by using an image obtained by image-taking the road around the subject vehicle by means of an image-taking means such as a camera installed on the subject vehicle.
2. Description of the Related Art
For example, when a vehicle (the subject vehicle) traveling on the road, such as a highway, with plural lanes changes the lane and simultaneously another vehicle is traveling in the vicinity in an adjacent lane and is catching up with the subject vehicle from the rear-and-side, if the subject vehicle carries out the change of the lane while not awaring of the existence of another vehicle, a big accident would occur.
And, when another vehicle travels behind the subject vehicle on the same lane as the subject vehicle with a higher speed and if the subject vehicle, for example, brakes suddenly, a collision would occur. Therefore, secure awareness of another vehicle in the vicinity is desirable.
Further, when the subject vehicle changes the lane and another vehicle slower than the subject vehicle is traveling obliquely ahead of the subject vehicle on the adjacent lane, there would also be a danger of collidation, which reqiures secure awareness of another vehicle in the vicinity.
A vehicle-use surroundings monitoring system disclosed in Japanese Patent Application Laid-open No.7-50769 is provided for solving the above problems. This vehicle-use surroundings monitoring system will be described in reference to FIGS. 9a-9d, which explain a change of a rear-and-side image obtained by a camera 1. FIGS. 9b,9c show images taken by the camera 1 of the subject vehicle at time t, t+xcex94t respectively.
When the subject vehicle goes straight on a flat road, for example a road sign and a building shown in FIG. 10a are imaged as shown in FIGS. 10b,10c at time t, t+xcex94t respectively. When corresponding points in the two images are searched and connected, velocity vectors, i.e. optical flows, shown in FIG. 10d are obtained. The prior art vehicle-use surroundings monitoring system detects the existence of another vehicle approaching the subject vehicle by monitoring a relative location between the subject vehicle and another vehicle traveling nearby by using the optical flow and raises an alarm.
Still another prior art uses two cameras, an edge point Pa of an object (not shown) is detected by examining the luminance difference between the neighboring pixels of the image taken by one of the cameras, and a corresponding point Pb (not shown), of the image taken by the other camera, corresponding to the detected edge point is detected. And, a position of the approaching vehicle with resprct to the subject vehicle is calculated based on the pixel coordinates of the points Pa and Pb, and an alarm informing of the existence of another vehicle approaching the subject vehicle is issued based on the above calculated position.
In still another prior art shown in FIG. 10, white lines of the lane on which the subject vehicle travels are detected by image-processing a taken-image, a cruising lane of the subject vehicle is distinguished from the adjacent lane area, and a detection of another vehicle is performed on each monitoring area, whereby it is judged whether another vehicle detected exists in the subject lane or the adjacent lane. In this case, since a monitoring area is limited, the processing time is reduced.
However, with respect to the above prior art of judging whether the approaching vehicle exists in the subject lane or the adjacent lane, there are problems stated below. As shown in FIG. 11a, when the following vehicle 100 is traveling after the subject vehicle with some distance, an adjacent vehicle 200 traveling far-off on the adjacent lane can be image-taken by the camera 1.
However, as shown in FIG. 11b, when the following vehicle 100 is traveling abnormally near the subject vehicle, the adjacent vehicle 200 cannot be image-taken with the camera 1.
When a state of the adjacent lane cannot be recognized with the image taken by the camera as stated above, the image of the following vehicle 100 overlapping with the adjacent lane area could be mis-detected as an adjacent vehicle 200. And, when the camera 1 is installed in order to image-take the front-and-side of the subject vehicle and when the subject vehicle is traveling abnormally near a front vehicle, the similar problem would arise.
In view of the foregoing, an object of the the present invention is to provide a vehicle-use surroundings monitoring system wherein a driver is prevented from driving without acknowledging that the detection of an approaching vehicle traveling in the adjacent lane area cannot be carried out by informing the driver of the existence of an abnormally approaching following vehicle obstructing to image-take the adjacent lanes.
In order to achieve the above object, as a first aspect of the present invention as shown in FIG. 1, a vehicle-use surroundings monitoring system comprises: an image-taking means 1 installed on a subject vehicle to take an image of surroundings of the subject vehicle to obtain a taken-image; an approaching vehicle detecting means 3a-1 to detect, by image-processing the taken-image, an approaching vehicle approaching the subject vehicle from an adjacent lane area; a danger judging means 3a-2 to judge dangerousness about the approaching vehicle detected; an existence judging means 3a-3 to judge an existence of an abnormally approaching following vehicle traveling on an subject lane ahead of or behind the subject vehicle and obstructing to image-take the adjacent lane area by the image-taking means; and an alarm generating means 5 to give out an alarm when the existence judging means judges that the abnormally approaching following vehicle exists.
According to the first aspect, because the alarm generating means informs that an image-taking of the adjacent lane by the image-taking means is obstructed so that the driver can recognize that the detection of an approaching vehicle traveling on the adjacent lane can not be carried out, the vehicle-use surroundings monitoring system can prevent the driver from driving without knowing that the detection of an approaching vehicle traveling in the adjacent lane area cannot be done.
As a second aspect of the present invention as shwon in FIG. 1, based on the first aspect, the existence judging means has an imaged vehicle detecting means 3a-31 to image-process the taken-image in order to detect an image-taken vehicle having been image-taken by the image-taking means, and the existence of the abnormally approaching following vehicle is judged based on the image-taken vehicle detected.
According to the second aspect, because the existence of an abnormally approached vehicle can be judged by detecting the abnormally approached vehicle based on the taken-image without providing an extra means other than the image-taking means, the vehicle-use surroundings monitoring system with reduced cost can be obtained.
As a third aspect of the present invention as shwon in FIG. 1, based on the second aspect, the imaged vehicle detecting means has a storing means 2d having stored vehicle images giving shape of respective vehicles, an extracting means 3a-311 to extract a vehicle candidate image to be a candidate of the image-taken vehicle from the taken-image, and a similarity calculating means 3a-312 to calculate a similarity-degree between the vehicle images and the vehicle candidate image, and the image-taken vehicle is detected when the similarity-degree is not less than a predetermined value.
According to the third aspect, because the similarity-degree of the vehicle candidate image against the vehicle images can be calculated, the vehicle-use surroundings monitoring system facilitating the detection of the vehicle can be obtained.
As a fourth aspect of the present invention, based on the third aspect, the storing means stores two or more kinds of vehicle images on one frame memory in order, and the similarity calculating means shifts the vehicle candidate image on the frame memory, executes a matching with each of the vehicle images, and calculates the similarity-degree.
According to the fourth aspect, because the matching is executed by shifting the vehicle candidate image over the frame memory on which two or more kinds of vehicle images are arranged, the calculation of the similarity-degree against the two or more kinds of vehicle images can be done with one matching processing for one vehicle candidate image, whereby the vehicle-use surroundings monitoring system attaining reducion of the similarity-degree calculation can be obtained.
As a fifth aspect of the present invention as shwon in FIG. 1, based on the first aspect, the vehicle-use surroundings monitoring system further comprises: an area specifyng means 3a-4 to specify an area, where an image-taking is obstructed by the abnormally approaching following vehicle, in the adjacent lane area when the existence judging means judges that the abnormally approaching following vehicle exists, and the danger judging means judges a degree of danger about the approaching vehicle traveling on the adjacent lane area except the area specified.
According to the fifth aspect, when there exists even a little area where the detection of an approaching vehicle is possible by the image-taking means in the adjacent lane areas, an approaching vehicle can be detected. Besides, an adjacent vehicle traveling in the adjacent lane can be prevented from being mis-detected as a just following vehicle or a preceding vehicle by judging the degree of danger about an approaching vehicle detected in the area where the image-taking is obstructed, whereby the vehicle-use surroundings monitoring system with improved reliability in judging dangerousness can be obtained.
As a sixth aspect of the present invention, based on the fifth aspect, an specifying by the area specifying means is executed before a detection by the approaching vehicle detecting means, and the approaching vehicle detecting means image-processes the adjacent lane area except the area specified and detects the approaching vehicle.
According to the sixth aspect, because the image processing is executed for the taken-image except the specified area, the vehicle-use surroundings monitoring system attaining reduction of the image processing can be obtained.
As a seventh aspect of the present invention as shwon in FIG. 1, based on any one of the first to sixth aspects, the approaching vehicle detecting means has an area setting means 3a-11 to set the adjacent lane area on the taken-image based on separation lines provided on a road surface and an optical flow detecting means 3a-12 to detect, as an optical flow, a movement of a same point in two adjacent lane areas obtained by the image-taking means with an interval of a specified time, and the danger judging means judges the dangerousness based on a size of the optical flow detected by the optical flow detecting means.
According to the seventh aspect, since the approaching vehicle can be detected on the basis of the size of the optical flow, two image-taking means does not need to be used, thereby attaining cost reduction.